Referring to FIG. 1, an axle 10 for a truck or other vehicle is typically assembled in a series of welding and machining steps shown in FIG. 2A, beginning at step 100. At step 105, two housing halves 12 are welded together to form an axle housing. At step 110, a carrier ring 14 is welded to the housing. At step 115, a cover 16 is welded to the housing. At step 120, the ends 18 of the axle housing are machined. At step 125, rough spindles 20 are welded to the machined ends 18. At step 130, rough brake flanges 22 are welded to the machined ends 18. At step 135, the axle housing is straightened, to compensate for any distortion that may have occurred during the various welding steps. At step 140, brackets 24 are welded to the axle housing. At step 145, the ring 14 is machined, including drilling one or more holes (not shown) that act as datums or precise reference points for the machining and positioning of other parts of the axle 10. At step 150, the spindles 20 are machine finished, with reference to the datums. At step 155, the flanges 22 are machine finished, with reference to the datums, so that the finished spindles 20 and flanges 22 are precisely aligned relative to each other. This alignment must respect tolerances on the order of a few thousandths of an inch, so that the brake drum (not shown) that will be mounted on the spindle 20 will be properly aligned with the brake shoe (not shown) that will be mounted on the flange 22 when the axle 10 is installed in the vehicle. At step 160, additional operations may optionally be performed on the finished axle, such as load testing of the welds, washing, painting and packing the axle for shipping. The process ends at step 165.
While this process is adequate for producing axles, it has a number of drawbacks. The multiple welding operations impart a large quantity of heat to the parts, resulting in distortion and possible misalignment of the spindles 20 and flanges 22. This distortion can be partially compensated for by straightening the axle 10 at step 120. However, the straightening operation causes metal fatigue and reduces the useful lifetime of the axle 10.
The distortion can also be partially compensated for by finishing the spindles 20 and flanges 22 after the welding operations are complete, based on the location of the datums. While this produces a satisfactory alignment between the parts, it is difficult to manipulate the fully-assembled axle in order to machine the spindles 20 and flanges 22, due to the large size and weight of the assembled axle 10. In particular, the mass of the cover is offset from the longitudinal axis of the axle 10, and causes the axle 10 to be unbalanced, making it even more difficult to manipulate and machine. In addition, machining a part as large as an assembled axle 10 requires a large amount of floor space, particularly when several machining operations are performed at several different stations within the assembly area, and the assembled axle is machined in a horizontal orientation, resulting in a high cost of manufacture. In addition, machining a large part requires large and expensive machinery, further adding to the cost of manufacture.
In addition, the added machining required to finish the spindles 20 and flanges 22 after the axle 10 is assembled results in increased manufacturing time, further increasing the cost of manufacture.
Therefore, there is a need for a method of manufacturing an axle that does not require straightening of the axle.
There is also a need for a method and apparatus for manufacturing an axle requiring a reduced amount of floor space.